Solar cell and production method thereof, photovoltaic module

ABSTRACT

Embodiments of the present disclosure relates to the field of solar cells, and in particular to a solar cell and a production method thereof, and a photovoltaic module. The solar cell includes: a P-type emitter formed on a first surface of an N-type substrate and including a first portion and a second portion, a top surface of the first portion includes first pyramid structures, and a top surface of the second portion includes second pyramid structures whose edges are straight. A transition surface is respectively formed on at least one edge of each first pyramid structure, and each of top surfaces of at least a part of the first pyramid structures includes a spherical or spherical-like substructure. A tunnel layer and a doped conductive layer sequentially formed over a second surface of the N-type substrate. The present disclosure can improve the photoelectric conversion performance of solar cells.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority under the ParisConvention to Chinese Patent Application No. 202210656583.8 filed onJun. 10, 2022, which is incorporated herein by reference in itsentirety.

TECHNIC FIELD

Embodiments of the present disclosure relates to the field of solarcells, and in particular to a solar cell and a production method for thesolar cell, and a photovoltaic module.

BACKGROUND

Solar cells have good photoelectric conversion capabilities. In solarcells, a diffusion process is required on the surface of silicon wafersto produce p-n junctions. In existing solar cells, boron diffusionprocesses are usually performed on the surface of silicon wafers to forman emitter on the surface of silicon wafers. On one hand, the emitterforms a p-n junction with the silicon wafer, and on the other hand, theemitter is also electrically connected with a metal electrode, so thatthe carriers transporting in the emitter can be collected by the metalelectrode. Therefore, the emitter has a great influence on thephotoelectric conversion performance of the solar cells.

The photoelectric conversion performance of the existing solar cells ispoor.

SUMMARY

Embodiments of the present disclosure provide a solar cell and aproduction method thereof, and a photovoltaic module, which is at leastconducive to the improvement of photoelectric conversion performance ofa solar cell.

Some embodiments of the present disclosure provide a solar cell,including: an N-type substrate, a P-type emitter formed on a firstsurface of the N-type substrate, and a tunnel layer and a dopedconductive layer sequentially formed over a second surface of the N-typesubstrate in a direction away from the N-type substrate. The P-typeemitter includes a first portion and a second portion, the first portionhas first pyramid structures formed on a top surface of the firstportion and the second portion has second pyramid structures formed on atop surface of the second portion. A transition surface is respectivelyformed on at least one edge of each first pyramid structure, thetransition surface is joined with two adjacent inclined surfaces of theeach first pyramid structure, and the transition surface is concave orconvex relative to a center of the each first pyramid structure. Asubstructure is formed on each of top surfaces of at least a part of thefirst pyramid structures, and a shape of the substructure is sphericalor spherical-like. Edges of each second pyramid structure are straight.A sheet resistance of the first portion ranges from 10 ohm/sq to 500ohm/sq, a doping concentration at the top surface of the first portionranges from 1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³. A sheet resistance of thesecond portion ranges from 100 ohm/sq to 1000 ohm/sq, and a dopingconcentration at the top surface of the second portion ranges from 1E¹⁶atoms/cm³ to 5E¹⁹ atoms/cm³.

In an example, heights of the first pyramid structures range from 0.1 μmto 5 μm, and sizes of bottoms of the first pyramid structures range from0.51 μm to 5 μm in any one dimension.

In an example, a doping element in the first portion of the P-typeemitter is of a same conductivity type as a doping element in the secondportion of the P-type emitter, and the doping element in the firstportion and the doping element in the second portion are each atrivalent element.

In an example, the doping element in the first portion and the dopingelement in the second portion each include boron or gallium.

In an example, the sheet resistance of the first portion is lower thanthe sheet resistance of the second portion.

In an example, the doping concentration at the top surface of the firstportion is not less than the doping concentration at the top surface ofthe second portion.

In an example, a junction depth of the first portion is not less than ajunction depth of the second portion.

In an example, a ratio of the junction depth of the first portion to thejunction depth of the second portion is not less than 2.

In an example, the junction depth of the first portion ranges from 0.2μm to 10 μm, and the junction depth of the second portion ranges from0.05 μm to 5 μm.

In an example, a difference between the doping concentration at the topsurface of the first portion and a doping concentration at a bottomsurface of the first portion ranges from 8E¹⁹ atoms/cm³ to 1E¹⁷atoms/cm³.

In an example, a difference between the doping concentration at the topsurface of the second portion and a doping concentration at a bottomsurface of the second portion ranges from 5E¹⁹ atoms/cm³ to 1E¹⁶atoms/cm³.

In an example, at least a part of at least one inclined surface of theeach first pyramid structure is concave or convex relative to a centerof the each first pyramid structure.

In an example, the solar cell further includes a first metal electrode,where the first metal electrode is formed on the first surface of theN-type substrate, and is electrically connected to the first portion ofthe P-type emitter.

In an example, a width of the first metal electrode is less than orequal to a width of the first portion of the P-type emitter.

Some embodiments of the present disclosure provide a production methodfor a solar cell, including: providing an N-type substrate, forming aP-type emitter on a first surface of the N-type substrate, and forming atunnel layer and a doped conductive layer sequentially over a secondsurface of the N-type substrate in a direction away from the N-typesubstrate. The P-type emitter includes a first portion and a secondportion, the first portion has first pyramid structures formed on a topsurface of the first portion and the second portion has second pyramidstructures formed on a top surface of the second portion. A transitionsurface is respectively formed on at least one edge of each firstpyramid structure, the transition surface is joined with two adjacentinclined surfaces of the each first pyramid structure, and thetransition surface is concave or convex relative to a center of the eachfirst pyramid structure. A substructure is formed on each of topsurfaces of at least a part of the first pyramid structures, and a shapeof the substructure is spherical or spherical-like. Edges of each secondpyramid structure are straight. A sheet resistance of the first portionranges from 10 ohm/sq to 500 ohm/sq, a doping concentration at the topsurface of the first portion ranges from 1E¹⁷ atoms/cm³ to 8E¹⁹atoms/cm³. A sheet resistance of the second portion ranges from 100ohm/sq to 1000 ohm/sq, and a doping concentration at the top surface ofthe second portion ranges from 1E¹⁶ atoms/cm³ to 5E¹⁹ atoms/cm³.

In an example, forming the P-type emitter includes: providing an N-typeinitial substrate; depositing a trivalent doping source on a top surfaceof the N-type initial substrate, where the trivalent doping sourceincludes a trivalent element; treating, by using a process of externalenergy source treatment, a preset region of the top surface of theN-type initial substrate, to diffuse the trivalent doping source treatedby the process of external energy source treatment into an interior ofthe N-type initial substrate; performing a high temperature treatment onthe N-type initial substrate to form the P-type emitter in the interiorof the N-type initial substrate, a top surface of the P-type emitter isexposed from the N-type initial substrate; forming the N-type substratein a region of the N-type initial substrate excluding the P-typeemitter; and forming the first portion of the P-type emitter in thepreset region of the N-type initial substrate, and forming the secondportion of the P-type emitter in a region of the P-type emitterexcluding the preset region.

In an example, depositing the trivalent doping source on the top surfaceof the N-type initial substrate includes forming a first thin film layerincluding the trivalent doping source under a temperature ranged from600° C. to 900° C., and a deposition time ranges from 20 s to 800 s; andperforming the high temperature treatment on the N-type initialsubstrate includes introducing, for a duration ranged from 5 minutes to300 minutes and under a temperature ranged from 800° C. to 1200° C.,oxygen of a flow rate ranged from 500 sccm to 50000 sccm to form asecond thin film layer, a thickness of the second thin film layer isgreater than a thickness of the first thin film layer.

In an example, the production method further includes forming a firstmetal electrode being electrically connected to the first portion of theP-type emitter.

Some embodiments of the present disclosure provide a photovoltaicmodule, including: a cell string formed by connecting a plurality ofsolar cells as described in any one of the above embodiments; anencapsulation layer configured to cover a surface of the cell string;and a cover plate configured to cover a surface of the encapsulationlayer facing away from the cell string.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are exemplarily illustrated in reference tocorresponding accompanying drawing(s), and these exemplary illustrationsdo not constitute limitations on the embodiments. Unless otherwisestated, the accompanying drawings do not constitute scale limitations.

FIG. 1 is a structural schematic diagram of a solar cell according to anembodiment of the present disclosure.

FIG. 2 is a partial enlarged view of the part marked with referencenumeral “1” in FIG. 1 .

FIG. 3 is another partial enlarged view of the part marked with thereference numeral “1” in FIG. 1 .

FIG. 4 is still another partial enlarged view of the part marked withthe reference numeral “1” in FIG. 1 .

FIG. 5 is a partial enlarged view of the part marked with referencenumeral “2” in FIG. 1 .

FIG. 6 is a structural schematic diagram of a photovoltaic moduleaccording to an embodiment of the present disclosure.

FIG. 7 is a structural schematic diagram corresponding to the operationof providing an N-type initial substrate in a production method for asolar cell according to an embodiment of the present disclosure.

FIG. 8 is a structural schematic diagram corresponding to the operationof forming a first thin film layer in the production method according toan embodiment of the present disclosure.

FIG. 9 is a structural schematic diagram corresponding to the operationof forming a first portion of the P-type emitter in the productionmethod according to an embodiment of the present disclosure.

FIG. 10 is a structural schematic diagram corresponding to the operationof forming a second thin film layer in the production method accordingto an embodiment of the present disclosure.

FIG. 11 is a structural schematic diagram corresponding to the operationof forming an anti-reflection layer in the production method accordingto an embodiment of the present disclosure.

FIG. 12 is a structural schematic diagram corresponding to the operationof forming a first metal electrode in the production method according toan embodiment of the present disclosure.

FIG. 13 is a structural schematic diagram corresponding to the operationof forming a tunnel layer and a doped conductive layer in the productionmethod according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It can be known from the background art that the existing solar cellshave a poor photoelectric conversion performance.

By analysis, it is found that one of the reasons for the poorphotoelectric conversion performance of the existing solar cells is thatthe emitter is usually electrically connected to a metal electrode, sothat the metal electrode can collect carriers in the emitter. In orderto reduce the contact resistance between the metal electrode and theemitter, the sheet resistance of the emitter should be reduced. Atpresent, in order to reduce the sheet resistance of the emitter, thedoping concentration of the emitter is usually increased. However, whenthe doping concentration of the emitter increases, the doping element inthe emitter becomes too much, so that the doping element in the emitterbecomes a strong recombination center, causing the increase of Augerrecombination. Thus, the passivation performance of the emitterdeteriorates, which in turn makes the photoelectric conversionperformance of the solar cell to be poor.

Embodiments of the present disclosure provide a solar cell, including aP-type emitter formed on a first surface of an N-type substrate. A firstportion has first pyramid structures formed on a top surface of thefirst portion of the P-type emitter. A transition surface isrespectively formed on at least one edge of each first pyramidstructure. The transition surface is joined with two adjacent inclinedsurfaces of the each first pyramid structure, and the transition surfaceis concave or convex relative to a center of the each first pyramidstructure. A substructure is formed on each of top surfaces of at leasta part of the first pyramid structures. In other words, each of at leasta part of the first pyramid structures has a micro-defect. Suchmicro-defect can form a certain crystal change, thereby forming a defectenergy level, so that the doping concentration of the first portion ofthe P-type emitter can be kept low while the sheet resistance of thefirst portion of the P-type emitter can be greatly reduced. In this way,the generation of Auger recombination can be reduced, and thephotoelectric conversion performance of the solar cell can be improved.Moreover, edges of each second pyramid structure of the second portionof the P-type emitter are straight, in other words, each second pyramidstructure is a normal pyramid structure. In this way, the sheetresistance of the second portion of the P-type emitter can be relativelyhigh, thereby reducing the generation of recombination centers andimproving the open-circuit voltage and short-circuit current of thesolar cell.

Embodiments of the present disclosure will be described in detail belowwith reference to the accompanying drawings. Those skilled in the artshould understand that, in the embodiments of the present disclosure,many technical details are provided for the reader to better understandthe present disclosure. However, even without these technical detailsand various modifications and variants based on the followingembodiments, the technical solutions claimed in the present disclosurecan be realized.

FIG. 1 is a structural schematic diagram of a solar cell according to anembodiment of the present disclosure, FIG. 2 is a partial enlarged viewof the part marked with reference numeral “1” in FIG. 1 , FIG. 3 isanother partial enlarged view of the part marked with the referencenumeral “1” in FIG. 1 , FIG. 4 is still another partial enlarged view ofthe part marked with the reference numeral “1” in FIG. 1 , and FIG. 5 isa partial enlarged view of the part marked with reference numeral “2” inFIG. 1 .

Referring to FIGS. 1 to 5 , the solar cell includes: an N-type substrate100, a P-type emitter 10 formed on a first surface of the N-typesubstrate 100, and a tunnel layer 150 and a doped conductive layer 160sequentially formed over a second surface of the N-type substrate 100 ina direction away from the N-type substrate 100. The P-type emitter 10includes a first portion 11 and a second portion 12, the first portion11 has first pyramid structures 1 formed on a top surface of the firstportion 11 and the second portion 12 has second pyramid structures 2formed on a top surface of the second portion 12. A transition surface13 is respectively formed on at least one edge of each first pyramidstructure 1, the transition surface 13 is joined with two adjacentinclined surfaces of the each first pyramid structure 1, and thetransition surface 13 is concave or convex relative to a center of theeach first pyramid structure 1. A substructure 14 is formed on each oftop surfaces of at least a part of the first pyramid structures 1, and ashape of the substructure 14 is spherical or spherical-like. Edges ofeach second pyramid structure 2 are straight. A sheet resistance of thefirst portion 11 ranges from 10 ohm/sq to 500 ohm/sq, a dopingconcentration at the top surface of the first portion 11 ranges from1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³. A sheet resistance of the secondportion 12 ranges from 100 ohm/sq to 1000 ohm/sq, and a dopingconcentration at the top surface of the second portion 12 ranges from1E¹⁶ atoms/cm³ to 5E¹⁹ atoms/cm³.

The N-type substrate 100 is used to receive incident light and generatephoto-generated carriers. In some embodiments, the N-type substrate 100may be an N-type silicon substrate 100, and the material of the N-typesilicon substrate may include at least one of monocrystalline silicon,polycrystalline silicon, amorphous silicon or microcrystalline silicon.The N-type substrate 100 is an N-type semiconductor substrate 100, thatis, the N-type substrate 100 is doped with N-type dopant ions, and theN-type dopant ions may be any one of phosphorus ions, arsenic ions, orantimony ions.

In some embodiments, the solar cell may be configured as a tunnel oxidepassivated contact (TOPCON) cell. The first surface and the secondsurface of the N-type substrate 100 are arranged opposite to each other,and both the first surface and the second surface of the N-typesubstrate 100 can be used to receive incident light or reflected light.In some embodiments, the first surface may be the back surface of theN-type substrate 100, and the second surface may be the front surface ofthe N-type substrate 100. In some other embodiments, the first surfacemay be the front surface of the N-type substrate 100, and the secondsurface may be the back surface of the N-type substrate 100.

In some embodiments, the second surface of the N-type substrate 100 maybe designed as a pyramid textured surface, so that the reflectivity ofthe second surface of the N-type substrate 100 to incident light is low,therefore the absorption and utilization rate of light is high. Thefirst surface of the N-type substrate 100 may be designed as anon-pyramid textured surface, such as in a stacked step form, so thatthe tunnel oxide layer 110 located on the first surface of the N-typesubstrate 100 has high density and uniformity, therefore the tunneloxide layer 110 has a good passivation effect on the first surface ofthe N-type substrate 100. In some embodiments, the first surface may bethe back surface of the N-type substrate 100, and the second surface maybe the front surface of the N-type substrate 100. In some otherembodiments, the first surface may be the front surface of the N-typesubstrate 100, and the second surface may be the back surface of theN-type substrate 100.

Referring to FIGS. 2 to 4 , the transition surface 13 is respectivelyformed on at least one edge of each first pyramid structure 1. It shouldbe understood that an edge refers to a strip-like bulge portion of afirst pyramid structure 1, i.e., a portion where adjacent inclinedsurfaces join of the first pyramid structure 1, and not only literallymeans “line”. In an example, a first pyramid structure has a bottomsurface and a plurality of inclined surfaces joined with the bottomsurface, two adjacent inclined surfaces join with each other, and atransition surface 13 is formed between the two adjacent inclinedsurfaces, that is to say, at least parts of the two adjacent inclinedsurfaces join with each other via the transition surface 13. In someembodiments, a transition surface 13 is formed on one edge of a firstpyramid structure 1, and the transition surface 13 may only be formed ona part of the edge, or may be formed on the entire edge. That is to say,two adjacent inclined surfaces of the first pyramid structure 1 areconnected by the transition surface 13. In some other embodiments, atransition surface 13 is respectively formed on a plurality of edges ofa first pyramid structure 1, and the transition surfaces 13 may only beformed on a part of an edge, or may be formed on the entire edge. Theembodiments of the present disclosure do not limit the specific positionof the transition surface 13 on an edge, as long as the transitionsurface 13 is formed on the edge.

It should be understood that the first pyramid structures 1 and thesecond pyramid structures 2 here are different from the texturedstructure. In the embodiments of the present disclosure, the siliconcrystal morphology of the first portion 11 of the P-type emitter 10 ischanged by forming the first pyramid structures 1 and the second pyramidstructures 2 on the surface of the P-type emitter 10, thereby changingthe performance of the first portion 11 of the P-type emitter 10.

As an example, a transition surface 13 is respectively formed on atleast one edge of each first pyramid structure 1, i.e. the at least oneedge of each first pyramid structure 1 has irregular deformation, and aspherical or spherical-like substructure 14 is formed on each of topsurfaces of at least a part of the first pyramid structures 1, so thatthe first pyramid structures 1 have micro-defects, and changes insilicon crystals are formed in the first portion 11 of the P-typeemitter. Furthermore, edges of each second pyramid structure 2 arestraight, in other words, there is no deformation in the edges of eachsecond pyramid structure 2. Due to the deformation in the at least oneedge of each first pyramid structure 1 and the deformation in each oftop surfaces of at least a part of the first pyramid structures 1, asheet resistance of the first portion 11 ranges from 10 ohm/sq to 500ohm/sq, and a doping concentration at the top surface of the firstportion 11 ranges from 1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³. Since there isno deformation in the edges of each second pyramid structure 2, a sheetresistance of the second portion 12 ranges from 100 ohm/sq to 1000ohm/sq, and a doping concentration at the top surface of the secondportion 12 ranges from 1E¹⁶ atoms/cm³ to 5E¹⁹ atoms/cm³. It is obviousthat the sheet resistance of the first portion 11 is much less than thesheet resistance of the second portion 12, but the doping concentrationat the top surface of the first portion 11 is not much different fromthe doping concentration at the top surface of the second portion 12. Itcan be seen that due to the micro-defects of the first pyramidstructures 1, the sheet resistance of the first portion 11 is much lessthan the sheet resistance of the second portion 12, thereby greatlyimproving ohmic contact of the first portion 11 of the P-type emitter10. Meanwhile, the doping concentration of the first portion 11 of theP-type emitter 10 is kept low, so that the generations of recombinationcenters in the first portion 11 of the P-type emitter 10 can be reduced,the good passivation effect of the P-type emitter 10 can be maintained,and the generations of Auger recombination can be reduced. In this way,the photoelectric conversion performance of the solar cell can beimproved. In some embodiments, heights of the first pyramid structures 1range from 0.1 μm to 5 μm, and sizes of the bottoms of the first pyramidstructures 1 range from 0.5 μm to 5 μm in any one dimension. It shouldbe understood that the larger the heights and the sizes of the bottomsof the first pyramid structures 1 in the first portion 11 of the P-typeemitter 10 in any one dimension are, the larger the overall sizes of thefirst pyramid structures 1 are, so that in a unit area, a number of thefirst pyramid structures 1 in the first portion 11 of the P-type emitter10 is smaller. The smaller the number of the first pyramid structures 1,the fewer the first pyramid structures with micro-defects, so thatdegree of the crystal deformation generated in the first portion 11 ofthe P-type emitter 10 is lower. Correspondingly, the smaller the sizesof the first pyramid structures 1 is, the greater the number of thefirst pyramid structures 1 in the first portion 11 of the P-type emitter10 per unit area, so that degree of the crystal deformation generated inthe first portion 11 of the P-type emitter 10 is higher. Based on this,the heights of the first pyramid structures 1 are set in a range of 0.1μm to 5 μm, and the sizes of the bottoms of the first pyramid structures1 are set in a range of 0.5 μm to 5 μm in any one dimension. In thisway, on one hand, the number of the first pyramid structures 1 isrelatively great, and the degree of the crystal deformation generated inthe first portion 11 of the P-type emitter 10 is relatively high, sothat a relatively high defect energy level is obtained, thereby leadingto a lower sheet resistance of the first portion 11 of the P-typeemitter 10, and improving the ohmic contact. On the other hand, withinthis range, excessive number of the first pyramid structures 1 in thefirst portion 11 of the P-type emitter 10 can be avoided, which canprevent the problem of forming an excessively high defect energy level,thereby forming strong recombination centers in the P-type emitter 10.In this way, the passivation performance of the first portion 11 of theP-type emitter 10 can be improved.

Referring to FIGS. 2 and 3 , a substructure 14 is further formed on eachof at least a part of the first pyramid structures 1. The existence ofthe substructures 14 makes the degree of the micro-defects in the firstpyramid structures 1 higher, so that the defect energy level formed inthe first portion 11 of the P-type emitter is higher, thereby furtherreducing the sheet resistance of the first portion 11 of the P-typeemitter 10.

Referring to FIGS. 1 and 5 , the edges of each second pyramid structure2 on the top surface of the second portion 12 are designed to bestraight, in other words, in each second pyramid structure 2, twoadjacent inclined surfaces are directly joined, and no deformationoccurs on the edges, so that a second pyramid structure 2 is a regulartetrahedron structure. That is to say, in the second portion 12 of theP-type emitter 10, no change occurs in the crystal structure. Thus, nodefect energy level is formed in the second portion 12 of the P-typeemitter thereby not only leading to a relatively high sheet resistanceof the second portion 12 of the P-type emitter 10, but also preventingthe formation of a large number of recombination centers in the secondportion 12 of the P-type emitter 10. In this way, a good passivationperformance of the second portion 12 of the P-type emitter 10 can bemaintained, the open-circuit voltage and short-circuit current of thesolar cell can be relatively high, and photoelectric conversionperformance of the solar cell can be improved.

Referring to FIG. 1 , in some embodiments, based on the differencesbetween the first pyramid structures 1 and the second pyramid structures2, the sheet resistance of the first portion 11 may be lower than thesheet resistance of the second portion 12. Since the edge(s) of a firstpyramid structure 1 deforms, and at least a part of the first pyramidstructures 1 further include substructures 14, defect energy level isformed in the first portion 11 of the P-type emitter 10, so that thesheet resistance of the first portion 11 of the P-type emitter 10 islow. While, the edges of each second pyramid structure 2 does notdeform, so that no defect energy level is formed in the second portion12 of the P-type emitter 10. Thus, the second portion 12 of the P-typeemitter 10 has a relatively high sheet resistance. In some embodiments,the sheet resistance of the first portion 11 may be 10 ohm/sq˜50 ohm/sq,50 ohm/sq˜75 ohm/sq, ohm/sq˜100 ohm/sq, 100 ohm/sq˜150 ohm/sq, 150ohm/sq˜200 ohm/sq, 200 ohm/sq˜300 ohm/sq, 300 ohm/sq˜400 ohm/sq or 400ohm/sq˜500 ohm/sq. The sheet resistance of the second portion 12 may be100 ohm/sq˜200 ohm/sq, 200 ohm/sq˜300 ohm/sq, 300 ohm/sq˜400 ohm/sq, 400ohm/sq˜500 ohm/sq, 500 ohm/sq˜700 ohm/sq, 700 ohm/sq˜850 ohm/sq, 850ohm/sq˜1000 ohm/sq. The sheet resistance of the first portion 11 of theP-type emitter 10 is much lower than that of the second portion 12, thusan improved ohmic contact of the first portion 11 of the P-type emitter10 can be obtained, which can reduce the contact resistance between thefirst portion 11 of the P-type emitter 10 and the metal electrode whenthe metal electrode is arranged to be in an electrical contact with thefirst portion 11 of the P-type emitter 10, thereby improving thetransport efficiency of carriers in the first portion 11 of the P-typeemitter 10 and the second portion 12 of the P-type emitter 10. Inaddition, by setting the resistance of the second portion 12 of theP-type emitter 10 to 100 ohm/sq˜1000 ohm/sq, the recombination ofcarriers in the second portion 12 of the P-type emitter 10 can besuppressed. In some embodiments, a recombination current in the secondportion 12 of the P-type emitter 10 is below 20 fA/cm², relatively lowrecombination current is conducive to reduction of recombination ofcarriers, thereby improving the passivation effect of the emitter. Inthis way, the open-circuit voltage, the short-circuit current and thephotoelectric conversion efficiency of the solar cell can be improved.

In some embodiments, the junction depth of the first portion 11 is notless than that of the second portion 12, that is to say, a thickness ofthe first portion 11 is relatively large. Thus, an electrical connectioncan be provided between the metal electrode and the first portion 11 ofthe P-type emitter 10, so that the problem that the paste for formingthe metal electrode penetrates the P-type emitter 10 and directlycontacts with the N-type initial substrate 100 during the sintering ofthe paste can be prevented. In addition, the junction depth of thesecond portion 12 is designed to be shallower, that is, a thickness ofthe second portion 12 of the P-type emitter 10 is relatively small, sothat the number of doping elements in the second portion 12 is less thanthe number of doping elements in the first portion 11. In other words,the doping concentration of the second portion 12 of the P-type emitter10 is lower. Therefore, compared with the first portion 11 of the P-typeemitter 10, the second portion 12 of the P-type emitter has a betterpassivation effect, which is conducive to reduction of the recombinationof carriers and improvement of the open-circuit voltage andshort-circuit current of the solar cell.

In some embodiments, a ratio of the junction depth of the first portion11 to the junction depth of the second portion 12 is not less than 2. Asan example, the ratio of the junction depth of the first portion 11 tothe junction depth of the second portion 12 ranges from 2 to 5. Forexample, the ratio can be 2, 2.5, 3, 3.5, 4, 4.5 or 5. The junctiondepth of the first portion 11 is much deeper than that of the secondportion 12, so that the junction depth of the first portion 11 of theP-type emitter 10 is deeper. In this way, when the metal electrode iselectrically connected with the first portion 11 of the P-type emitter10, it can be ensured that the paste will not burn through the firstportion 11 of the p-type emitter 10 during the sintering, so as toprevent the problem of damaging the p-n junction due to the contactbetween the metal electrode and the N-type substrate 100, therebyensuring good photoelectric conversion performance of the solar cell.

In some embodiments, the junction depth of the first portion 11 rangesfrom 0.2 μm to 10 μm, and the junction depth of the second portion 12ranges from 0.05 μm to 5 μm. Within this range, the junction depth ofthe first portion 11 is not too deep, so as to avoid the problem thatcontent of doping element in the first portion 11 of the P-type emitter10 is too high due to excessive thickness of the first portion 11 toform a strong recombination center. Moreover, within this range, thejunction depth of the second portion 12 is relatively shallow, and thereare relatively few doping elements in the second portion 12 of theP-type emitter 10, so that a good passivation effect of the P-typeemitter 10 can be maintained.

In some embodiments, a doping element in the first portion 11 of theP-type emitter 10 is of a same conductivity type as a doping element inthe second portion 12 of the P-type emitter 10, and the doping elementin the first portion 11 and the doping element in the second portion 12are each a trivalent element. In other words, each of the first portion11 of the P-type emitter 10 and the second portion 12 of the P-typeemitter 10 includes only one of the trivalent elements, i.e. the firstportion 11 and the second portion 12 are doped with a single element.Thus, the first portion 11 and the second portion 12 of the P-typeemitter 10 include no impurity element, thereby preventing the problemof carrier recombination due to impurity elements becoming recombinationcenters.

In some embodiments, the doping element in the first portion 11 and thedoping element in the second portion 12 each include boron element orgallium element. The first portion 11 and the second portion 12 aredesigned to include only one kind of doping element, so that the firstportion 11 and the second portion 12 of the P-type emitter 10 becomehigh-efficiency doping layers, thus there is no impurity element in thefirst portion 11 and the second portion 12 of the P-type emitter 10, oran amount of the impurity element is very small. In this way, theproblem of the impurity element becoming a recombination center can beavoided, thereby suppressing the recombination of carriers andincreasing the number of carriers.

In some embodiments, the doping concentration at the top surface of thefirst portion 11 is not less than the doping concentration at the topsurface of the second portion 12 of the P-type emitter 10. Since thejunction depth of the first portion 11 is larger than that of the secondportion 12, the first portion 11 of the P-type emitter 10 includes moredoping elements. In some embodiments, the doping concentration at thetop surface of the first portion 11 may be 1E¹⁷ atoms/cm³ to 7E¹⁷atoms/cm³, 7E¹⁷ atoms/cm³ to 1E¹⁸ atoms/cm³, 1E¹⁸ atoms/cm³ to 6E¹⁸atoms/cm³, 6E¹⁸ atoms/cm³ to 1E¹⁹ atoms/cm³ or 1E¹⁹ atoms/cm³ to 8E¹⁹atoms/cm³; and the doping concentration at the top surface of the secondportion 12 may be 1E¹⁶ atoms/cm³ to 1E¹⁷ atoms/cm³, 1E¹⁷ atoms/cm³ to1E¹⁸ atoms/cm³, 1E¹⁸ atoms/cm³ to 1E¹⁹ atoms/cm³ or 1E¹⁹ atoms/cm³ to5E¹⁹ atoms/cm³. The doping concentration at the top surface of the firstportion 11 is designed to be relatively high, which can ensure that thesheet resistance of the first portion 11 is relatively low. Meanwhile,the doping concentration at the top surface of the second portion 12 isdesigned to be relatively low, which can avoid that excessive dopingelements become recombination centers due to there being too many dopingelements in the second portion 12. In this way, the recombination ofcarriers can be suppressed and the short-circuit current andopen-circuit voltage of the solar cell can be improved. It is can beseen that the doping concentration at the top surface of the firstportion 11 is relatively close to the doping concentration at the topsurface of the second portion 12. In some embodiments, the dopingconcentration at the top surface of the first portion 11 may be equal tothe doping concentration at the top surface of the second portion 12.Thus, the doping concentration at the top surface of the first portion11 is reduced, and the sheet resistance of the first portion 11 is muchless than that of the second portion 12. In this way, both a relativelylow sheet resistance of the first portion 11 and a relatively low dopingconcentration of the first portion 11 can be achieved, thereby improvingthe ohmic contact of the P-type emitter 10 and maintaining a goodpassivation effect of the P-type emitter 10.

In some embodiments, in a direction from the top surface of the P-typeemitter 10 to the bottom surface of the P-type emitter 10, the dopingconcentration in the interior of the first portion 11 of the P-typeemitter 10 gradually decreases, and the doping concentration in theinterior of the second portion 12 of the P-type emitter 10 graduallydecreases. That is to say, each of the first portion 11 of the P-typeemitter 10 and the second portion 12 of the P-type emitter 10 has adescending doping concentration gradient, which is conducive to thetransport of carriers in the first portion 11 of the P-type emitter 10and the second portion 12 of the P-type emitter 10 from a region with arelatively high concentration to a region with a relatively lowconcentration, until into the N-type substrate 100. In this way, thetransport speed of carriers can be increased and the open-circuitvoltage of the solar cell can be improved.

In some embodiments, the difference between the doping concentration atthe top surface of the first portion 11 and the doping concentration atthe bottom surface of the first portion 11 is 8E¹⁹ atoms/cm³ to 1E¹⁷atoms/cm³. Within this range, on one hand, the difference in dopingconcentration in the interior of the first portion 11 of the P-typeemitter 10 is relatively high, thereby facilitating the transport ofcarriers. On the other hand, it can be prevented that the difference indoping concentration in the interior of the first portion 11 of theP-type emitter 10 is too small, thereby preventing an excessive overalldoping concentration of the first portion 11 due to the small differencebetween the doping concentration at the top surface and the dopingconcentration in the first portion 11.

In some embodiments, the difference between the doping concentration atthe top surface of the second portion 12 and the doping concentration atthe bottom surface of the second portion 12 is 5E¹⁹ atoms/cm³ to 1E¹⁶atoms/cm³. Within this range, the doping concentration in the interiorof the second portion 12 of the P-type emitter 10 will not be too low,so that the normal transport of carriers in the second portion 12 of theP-type emitter 10 can be ensured. In addition, within this range, theoverall doping concentration of the second portion 12 of the P-typeemitter 10 can be kept low, thus Auger recombination can be preventedfrom occurring in the second portion 12 of the P-type emitter 10.

In some embodiments, at least a part of at least one inclined surface ofthe first pyramid structure 1 is concave or convex relative to a centerof the first pyramid structure 1, that is to say, at least one inclinedsurface of the first pyramid structure 1 has irregular deformation. Thisirregular deformation leads to dislocations and dangling bonds in thefirst portion 11 of the P-type emitter 10, thereby forming a deep energylevel in interior of the first portion 11 of the P-type emitter 10, thusfurther reducing the sheet resistance of the first portion 11 of theP-type emitter 10.

In some embodiments, the ratio of a width of the second portion 12 to awidth of the first portion 11 is greater than 5.6. That is to say, thesecond portion 12 of the P-type emitter 10 with relatively higher sheetresistance accounts for a higher proportion, since the second portion 12of the P-type emitter 10 has better passivation performance and cansuppress the recombination of carriers, the overall passivationperformance of the P-type emitter 10 is good. Furthermore, since thefirst portion 11 of the P-type emitter 10 only needs to be electricallyconnected to the metal electrode to improve the ohmic contact with themetal electrode, the width of the first portion 11 of the P-type emitter10 can be set to be small, so as to improve the ohmic contact andmaintain relatively good passivation performance of the emitter.

In some embodiments, the solar cell further includes a first metalelectrode 140, the first metal electrode 140 is formed on the firstsurface of the N-type substrate 100 and is electrically connected to thefirst portion 11 of the P-type emitter 10. Since the carriers in theP-type emitter 10 will transport to the first metal electrode 140electrically connected to the first portion 11 of the P-type emitter 10,and the sheet resistance of the first portion 11 of the P-type emitter10 is relatively low, so that the contact resistance between the firstportion 11 of the P-type emitter 10 and the first metal electrode 140 islow. In some embodiments, the metal recombination current in the firstportion 11 of the P-type emitter 10 can be as high as 700 fA/cm²,thereby increasing the transport rate of carriers in the P-type emitter10 to the first metal electrode 140. In addition, since the firstportion 11 of the P-type emitter 10 has a relatively deep junctiondepth, the conductive paste does not easily penetrate the first portion11 of the P-type emitter 10 during the preparation of the first metalelectrode 140. In this way, damage to the structure of the p-n junctioncan be avoided, which is conducive to maintenance of the goodphotoelectric conversion performance of the solar cell.

In some embodiments, a width of the first metal electrode 140 is lessthan or equal to the width of the first portion 11 of the P-type emitter10, so that the first metal electrode 140 can be encapsulated by thefirst portion 11 of the P-type emitter 10, i.e. the side surfaces andthe bottom surface of the first metal electrode 140 are in contact withthe first portion 11 of the P-type emitter 10. Since the sheetresistance of the first portion 11 of the P-type emitter 10 isrelatively lower, the contact resistance between the first metalelectrode 140 and the P-type emitter 10 can be further improved bydesigning the first metal electrode 140 to be encapsulated by the firstportion 11 of the P-type emitter 10, thereby improving the collectionefficiency of carriers by the first metal electrode 140.

In some embodiments, the solar cell further includes an anti-reflectionlayer 130 located on the top surface of the P-type emitter 10, and thefirst metal electrode 140 penetrates the anti-reflection layer 130 toelectrically connect to the P-type emitter 10. The anti-reflection layer130 is used for reducing reflection of incident light by the substrate.In some embodiments, the anti-reflection layer 130 may be a single-layerstructure or a multi-layer structure, and the material of theanti-reflection layer 130 may be at least one of magnesium fluoride,silicon oxide, aluminum oxide, silicon oxynitride, silicon nitride, andtitanium oxide.

The tunnel layer 150 is used to achieve interface passivation of thesecond surface of the substrate. In some embodiments, the material ofthe tunnel layer 150 may be a dielectric material, such as any one ofsilicon oxide, magnesium fluoride, silicon oxide, amorphous silicon,polycrystalline silicon, silicon carbide, silicon nitride, siliconoxynitride, aluminum oxide and titanium oxide.

The doped conductive layer 160 is used to form field passivation. Insome embodiments, the material of the doped conductive layer 160 may bedoped silicon. In some embodiments, the doped conductive layer 160 andthe substrate include doping elements of the same conductivity type. Thedoped silicon may include one or more of N-type doped polysilicon,N-type doped microcrystalline silicon and N-type doped amorphous siliconand silicon carbide.

In some embodiments, the solar cell further includes a first passivationlayer 170 located on a surface of the doped conductive layer 160 awayfrom the substrate. In some embodiments, the material of the firstpassivation layer 170 may be one or more of magnesium fluoride, siliconoxide, aluminum oxide, silicon oxynitride, silicon nitride and titaniumoxide. In some embodiments, the first passivation layer 170 may be asingle-layer structure. In some other embodiments, the first passivationlayer 170 may be a multi-layer structure.

In some embodiments, the solar cell further includes a second metalelectrode 180 penetrating the first passivation layer 170 to form anelectrical connection with the doped conductive layer 160.

In the solar cell as described in the above embodiments, a P-typeemitter 10 is formed on a first surface of an N-type substrate 100. Afirst portion 11 has first pyramid structures 1 formed on the firstportion 11 of the P-type emitter 10. A transition surface 13 isrespectively formed on at least one edge of each first pyramid structure1. The transition surface 13 is joined with two adjacent inclinedsurfaces of the each first pyramid structure 1, and the transitionsurface 13 is concave or convex relative to a center of the each firstpyramid structure 1. A substructure 14 is formed on each of top surfacesof at least a part of the first pyramid structures 1. In other words,each of at least a part of the first pyramid structures 1 has amicro-defect. Such micro-defect can form a certain crystal change,thereby forming a defect energy level, so that the doping concentrationof the first portion 11 of the P-type emitter 10 can be kept low whilethe sheet resistance of the first portion 11 of the P-type emitter 10can be greatly reduced. In this way, the generation of Augerrecombination can be reduced, and the photoelectric conversionperformance of the solar cell can be improved. Moreover, edges of eachsecond pyramid structure 2 of the second portion 12 of the P-typeemitter 10 are straight, in other words, a second pyramid structure is anormal pyramid structure. In this way, the sheet resistance of thesecond portion 12 of the P-type emitter 10 can be relatively high,thereby reducing the generation of recombination centers and improvingthe open-circuit voltage and short-circuit current of the solar cell.

Embodiments of the present disclosure further provide a photovoltaicmodule, referring to FIG. 6 , the photovoltaic module includes: a cellstring formed by connecting a plurality of solar cells 101 as providedin the above embodiments; an encapsulation layer 102 used for covering asurface of the cell string; and a cover plate 103 used for covering asurface of the encapsulation layer 102 facing away from the cell string.The solar cells 101 are electrically connected in a form of a singlepiece or multiple pieces to form a plurality of cell strings, and theplurality of cell strings are electrically connected in series and/orparallel.

In some embodiments, the plurality of cell strings may be electricallyconnected by conductive strips 104. The encapsulation layer 102 coversthe front and back surfaces of the solar cell 101. As an example, theencapsulation layer 102 may be an organic encapsulation adhesive film,such as an adhesive film of ethylene-vinyl acetate copolymer (EVA), anadhesive film of polyethylene octene co-elastomer (POE) or an adhesivefilm of polyethylene terephthalate (PET) and the like. In someembodiments, the cover plate 103 may be a cover plate 103 with alight-transmitting function, such as a glass cover plate, a plasticcover plate, or the like. As an example, the surface of the cover plate103 facing the encapsulation layer 102 may be a concave-convex surface,thereby increasing the utilization rate of incident light.

Another embodiment of the present disclosure further provides aproduction method for a solar cell, the solar cell as provided in theabove embodiments can be obtained by implementing the method. Theproduction method provided by this embodiment of the present disclosurewill be described in detail below with reference to the accompanyingdrawings.

FIGS. 7 to 13 are structural schematic diagrams corresponding to theoperations of the production method for the solar cell provided by thisembodiment of the present disclosure.

An N-type substrate 100 is provided.

The N-type substrate 100 is used to receive incident light and generatephoto-generated carriers. In some embodiments, the N-type substrate 100may be an N-type silicon substrate, and the material of the N-typesilicon substrate may include at least one of monocrystalline silicon,polycrystalline silicon, amorphous silicon or microcrystalline silicon.The N-type substrate 100 is an N-type semiconductor substrate, that is,the N-type substrate 100 is doped with N-type dopant ions, and theN-type dopant ions may be any one of phosphorus ions, arsenic ions, orantimony ions.

Referring to FIGS. 7 to 11 , a P-type emitter 10 is formed on a firstsurface of the N-type substrate 100, the P-type emitter 10 includes afirst portion 11 and a second portion 12, first pyramid structures 1 areformed on a top surface of the first portion 11, a transition surface 13is respectively formed on at least one edge of each first pyramidstructure 1, the transition surface 13 is joined with two adjacentinclined surfaces of the each first pyramid structure 1, and thetransition surface 13 is concave or convex relative to a center of theeach first pyramid structure 1. A substructure 14 is formed on each oftop surfaces of at least a part of the first pyramid structures 1, and ashape of the substructure 14 is spherical or spherical-like. Secondpyramid structures 2 are formed on a top surface of the second portion12, edges of each second pyramid structure 2 are straight. A sheetresistance of the first portion 11 ranges from 10 ohm/sq to 500 ohm/sq,a doping concentration at the top surface of the first portion 11 rangesfrom 1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³, a sheet resistance of the secondportion 12 ranges from 100 ohm/sq to 1000 ohm/sq, and a dopingconcentration at the top surface of the second portion 12 ranges from1E¹⁶ atoms/cm³ to 5E¹⁹ atoms/cm³.

A transition surface 13 is respectively formed on at least one edge ofeach formed first pyramid structure 1, i.e. the at least one edge ofeach first pyramid structure 1 has irregular deformation, and aspherical or spherical-like substructure 14 is formed on each of topsurfaces of at least a part of the first pyramid structures 1, so thatthe first pyramid structures 1 have micro-defects, and changes insilicon crystals are formed in the first portion 11 of the P-typeemitter. Furthermore, edges of each second pyramid structure 2 arestraight, in other words, there is no deformation in the edges of eachsecond pyramid structure 2. Due to the deformation in the at least oneedge of each first pyramid structure 1 and the deformation in each oftop surfaces of at least a part of the first pyramid structures 1, asheet resistance of the first portion 11 ranges from 10 ohm/sq to 500ohm/sq, and a doping concentration at the top surface of the firstportion 11 ranges from 1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³. Since there isno deformation in the edges of each second pyramid structure 2, a sheetresistance of the second portion 12 ranges from 100 ohm/sq to 1000ohm/sq, and a doping concentration at the top surface of the secondportion 12 ranges from 1E¹⁶ atoms/cm³ to 5E¹⁹ atoms/cm³. It is obviousthat the sheet resistance of the first portion 11 is much less than thesheet resistance of the second portion 12, but the doping concentrationat the top surface of the first portion 11 is not much different fromthe doping concentration at the top surface of the second portion 12. Itcan be seen that due to the micro-defects of the first pyramidstructures 1, the sheet resistance of the first portion 11 is much lessthan the sheet resistance of the second portion 12, thereby greatlyimproving ohmic contact of the first portion 11 of the P-type emitter10. Meanwhile, the doping concentration of the first portion 11 of theP-type emitter 10 is kept low, so that the generations of recombinationcenters in the first portion 11 of the P-type emitter 10 can be reduced,the good passivation effect of the P-type emitter 10 can be maintained,and the generations of Auger recombination can be reduced. In this way,the photoelectric conversion performance of the solar cell can beimproved.

In some embodiments, a method for forming the P-type emitter 10 includesthe following operations.

Referring to FIG. 7 , an N-type initial substrate 20 is provided, andthe N-type initial substrate 20 is used as a basis for forming theN-type substrate 100 and the P-type emitter 10. Therefore, the materialsof the N-type initial substrate 20 and the N-type substrate 100 may beof the same.

In some embodiments, a first surface of the N-type initial substrate 20may be designed as a pyramid textured surface, so that the reflectivityof a first surface of the N-type initial substrate 20 to incident lightis low, and the absorption and utilization rate of light is high. Insome embodiments, the N-type initial substrate 20 is an N-type initialsemiconductor substrate, that is, the N-type initial substrate 20 isdoped with N-type dopant ions, and the N-type dopant ions may be any oneof phosphorus ions, arsenic ions, or antimony ions.

The method for forming the P-type emitter 10 further includes, referringto FIGS. 8 and 9 , depositing a trivalent doping source on a top surfaceof the N-type initial substrate 20. The trivalent doping source includesa trivalent element. The trivalent doping source located on the topsurface of the N-type initial substrate 20 is used to be subsequentlydiffused into the N-type initial substrate 20 to form the P-type emitter10. The trivalent doping source is designed to include a trivalentelement, i.e. the N-type initial substrate 20 is doped with a singleelement, so that the formed P-type emitter 10 includes an element of asingle type, and therefore becomes a high-efficiency doping layer. It isdesigned that there is no impurity element in the first portion 11 ofthe P-type emitter 10 and the second portion 12 of the P-type emitter10, or an amount of the impurity element is very small. In this way, theproblem that recombination of carriers occurs due to the impurityelement becoming a recombination center can be avoided. In someembodiments, the trivalent doping source may be a boron source, and mayfor example be boron trichloride or boron tribromide.

Referring to FIG. 8 , in some embodiments, depositing the trivalentdoping source on the top surface of the N-type initial substrate 20includes forming a first thin film layer 110. The first thin film layer110 includes the trivalent dopant source and at least one of boronelement, oxygen element, silicon element or chlorine element. Adeposition time ranges from 20 s to 800 s, and a temperature ranges from600° C. to 900° C. In some embodiments, when the trivalent doping sourceis a boron source, the main components of the first thin film layer 110may include silicon oxide and boron oxide, and the trivalent dopingsource may be stored in the first thin film layer 110 in a form of boronoxide. Since silicon oxide has high hardness, it can protect the N-typeinitial substrate 20 during the doping process.

In addition, since the thickness of the first thin film layer 110 isrelatively small, when a relatively thin first thin film layer 110includes relatively many trivalent doping sources, the trivalent dopingsources aggregates in the first thin film layer 110, thereby increasingthe concentration of the trivalent doping source. In this way, when thetrivalent doping source is subsequently diffused into the N-type initialsubstrate 20 by the doping process, the doping process is facilitatedand it is easier to form the first portion 11 of the P-type emitter 10with relatively high doping concentration, thereby reducing the sheetresistance of the first portion 11 of the P-type emitter 10. Inaddition, since the thickness of the first thin film layer 110 isrelatively small, the trivalent doping source that can be included inthe first thin film layer 110 will not be too much, so that excessivetrivalent doping source elements can prevented from being doped into theN-type initial substrate 20. In this way, the problem that relativelymany trivalent doping source elements become strong recombinationcenters due to too many trivalent doping source elements being containedin the N-type initial substrate 20, which leads to poor passivationcapability of the formed first portion 11 of the P-type emitter 10 canbe prevented.

In some embodiments, a method for forming the first thin film layer 110may include depositing a trivalent doping source on the first surface ofthe N-type initial substrate 20. In some embodiments, boron trichloridemay be deposited, as the trivalent doping source, on the first surfaceof the N-type initial substrate 20 by chemical vapor deposition or spincoating.

As an example, the method for forming the first thin film layer 110 mayinclude: performing a boat feeding process on the N-type initialsubstrate 20; after the boat feeding process of the N-type initialsubstrate 20, raising a temperature to a first preset temperature, anddepositing a trivalent doping source on the first surface of the N-typeinitial substrate 20, the first preset temperature may be 500° C. to900° C.; then raising the temperature to a second preset temperature,the second preset temperature is greater than the first presettemperature, for example, the second preset temperature may be 900° C.to 1300° C.; and performing a junction pushing process in a nitrogenatmosphere, which can improve the density and uniformity of the formedfirst thin film layer 110. In some embodiments, while depositing thetrivalent doping source, a small amount of oxygen may be introduced, forexample, 100 sccm to 2000 sccm, which is conducive to the furtherformation of a first thin film layer 110 with relatively high density.

Referring to FIG. 9 , after depositing the trivalent dopant source, apreset region of the top surface of the N-type initial substrate 20 istreated using a process of external energy source treatment, and thetrivalent dopant source treated by the process of external energy sourcetreatment is diffused into an interior of the N-type initial substrate20 to form the first portion 11 of the P-type emitter 10 in the presetregion of the N-type initial substrate 20, and a top surface of thefirst portion 11 of the P-type emitter 10 is exposed from the N-typeinitial substrate 20. The process of external energy source treatment isperformed on the preset region, so that the trivalent doping source inthe preset region of the first thin film layer 110 is diffused into theinterior of the N-type initial substrate 20. At the same time, with theprocess of external energy source treatment, the structure of the presetregion at the top surface of the N-type initial substrate 20 is changedto form the first pyramid structures 1. It is noted that the structureof the N-type initial substrate 20 is a regular tetrahedral structurebefore performing the process of external energy source treatment. Afterthe process of external energy source treatment, at least one edge ofeach first pyramid structure 1 deforms to form a transition surface 13,and a substructure is formed on each of top surfaces of at least a partof the first pyramid structures. After the preset region of the N-typeinitial substrate 20 is doped with the trivalent doping source, the topsurface of the formed first portion 11 of the P-type emitter 10 has thefirst pyramid structures 1. In this way, a deep energy level can beformed in the first portion 11 of the P-type emitter 10, thus the sheetresistance of the first portion 11 of the P-type emitter 10 can bereduced.

In some embodiments, the process of external energy source treatmentincludes a laser doping process. In the laser doping process, awavelength of the laser ranges from 300 nm to 1000 nm, for example, 300nm to 500 nm, 500 nm to 750 nm, 750 nm to 900 nm, or 900 nm to 1000 nm.By controlling a focal position and laser wavelength of the laserparameters, structural morphologies at different positions of the firstpyramid structures 1 can be changed. In addition, due to the simpleoperation of the laser process, the laser parameters are easy tocontrol, so that the morphologies of the formed first pyramid structures1 is as expected. By setting the wavelength and energy density of thelaser within this range, deformation occurs on at least one edge of eachfirst pyramid structure 1, and a spherical or spherical-likesubstructure 14 is formed on each of top surfaces of at least a part ofthe first pyramid structures 1. Due to the micro-defects of the formedfirst pyramid structures 1, crystal changes are formed in the firstportion 11 of the P-type emitter 10, thereby forming a defect energylevel, so that the doping concentration of the first portion 11 of theP-type emitter 10 can be kept low while the sheet resistance of thefirst portion 11 can be greatly reduced. In this way, not only the ohmiccontact can be greatly improved, but also a good passivation effect ofthe first portion 11 of the P-type emitter 10 can be maintained, and theshort-circuit voltage and open-circuit current of the solar cell can beimproved.

In another embodiment, the process of external energy source treatmentmay also include plasma irradiation or a directional ion implantationprocess.

In some embodiments, after forming the first portion 11 of the P-typeemitter 10, the method further includes: performing a cleaning operationon the first surface of the N-type initial substrate 20 to remove thefirst thin film layer 110. In this way, the remaining trivalent dopingsources in the first thin film layer 110 and the adsorbed impurities onthe surface of the N-type initial substrate 20 can be removed, which isconducive to prevention of leakage. Furthermore, the first thin filmlayer 110 contains a large number of trivalent doping sources, and thesetrivalent doping sources will be converted into non-activated trivalentdoping sources, such as non-activated boron, in the subsequent hightemperature process for forming the second thin film layer. Theexistence of the non-activated trivalent doping sources will increasethe recombination of carriers on the surface of the N-type initialsubstrate 20, thereby affecting the photoelectric conversion efficiencyof the solar cell. Therefore, removing the first thin film layer 110before the operation of forming the second thin film layer can alsoreduce the content of the non-activated trivalent doping sources on thesurface of the N-type initial substrate 20 after subsequently formingthe second thin film layer, thereby reducing the recombination ofcarriers on the surface of the N-type initial substrate 20 and improvingthe photoelectric conversion efficiency of the solar cell. As anexample, the cleaning operation may include cleaning the surface of theN-type initial substrate 20 with alkali solution or acid solution, wherethe alkali solution may be at least one of KOH or H₂O₂ aqueous solution,and the acid solution may be at least one of HF or HCl aqueous solution.

After forming the first portion 11 of the P-type emitter 10, referringto FIGS. 10 to 11 , a high temperature treatment is performed on theN-type initial substrate 20 to form the P-type emitter 10 in the N-typeinitial substrate 20, and the top surface of the P-type emitter 10 isexposed from the N-type initial substrate 20. As an example, the N-typesubstrate 100 is formed in a region of the N-type initial substrate 20excluding the P-type emitter 10, and the second portion 12 of the P-typeemitter 10 is formed in a region of the P-type emitter 10 excluding thepreset region. Since the process of external energy source treatment isonly performed on the surface of the preset region of the N-type initialsubstrate 20, the trivalent doping sources in the first thin film layer110 corresponding to the preset region are diffused into the interior ofthe N-type initial substrate 20. Thus, the junction depth of the formedfirst portion 11 of the P-type emitter 10 is greater than the junctiondepth of the second portion 12 of the P-type emitter 10. Thus, the metalelectrode can be arranged to be in electrical connection with the firstportion 11 of the P-type emitter 10. In this way, the problem that thepaste for forming the metal electrode penetrates the P-type emitter 10and directly contacts with the N-type initial substrate 20 during thesintering process can be prevented. Moreover, the junction depth of thesecond portion 12 is designed to be shallow, that is, the thickness ofthe second portion 12 of the P-type emitter 10 is small, so that thenumber of doping elements in the second portion 12 is less than thenumber of doping elements in the first portion 11, that is, the dopingconcentration of the second portion 12 of the P-type emitter 10 islower. Therefore, compared with the first portion 11 of the P-typeemitter 10, the second portion 12 of the P-type emitter 10 has a betterpassivation effect, which is conducive to reduction of the recombinationof carriers and to improvement of the open-circuit voltage andshort-circuit current of the solar cell.

After performing the high temperature treatment on the N-type initialsubstrate 20, part of the trivalent doping sources is doped into theN-type initial substrate 20, so that part of the N-type initialsubstrate 20 is transformed into the second portion 12 of the P-typeemitter 10. That is to say, the portion of the N-type initial substrate20 excluding the first portion 11 of the P-type emitter 10 and thesecond portion 12 of the P-type emitter 10 corresponds to the N-typesubstrate 100.

Referring to FIG. 10 , in some embodiments, in the operation ofperforming the high temperature treatment on the N-type initialsubstrate 20, oxygen of a flow rate of 500 sccm to 50000 sccm isintroduced for a duration ranged from 5 mins to 300 mins and under atemperature ranged from 800° C. to 1200° C., to form a second thin filmlayer 120. A thickness of the second thin film layer 120 is smaller thana thickness of the first thin film layer 110. The amount of the oxygenintroduced in the process of forming the second thin film layer 120 isrelatively large, so that the oxygen can react with more trivalentdoping sources, thus the thickness of the formed second thin film layer120 is larger than the thickness of the first thin film layer 110. Inthis way, on one hand, when the thinner first thin film layer 110includes more trivalent doping sources, the trivalent doping sourcesaggregate in the first thin film layer 110, thereby increasing theconcentration of the trivalent doping sources, which is conducive to thelaser doping, and because the first thin film layer 110 is relativelythin, it is easy for the laser to penetrate into the N-type initialsubstrate 20. On the other hand, the second thin film layer 120 isthicker, which can ensure that the amount of trivalent doping sourcesabsorbed by the second thin film layer 120 in a region excluding thepreset region of the first surface of the N-type initial substrate 20 isrelatively large. In this way, the doping concentration at the topsurface of the first portion 11 of the P-type emitter 10 and the dopingconcentration at the top surface of the second portion 12 of the P-typeemitter 10 can be reduced, and the passivation performance can beimproved.

Referring to FIG. 11 , in some embodiments, the method further includes:performing the cleaning operation on the N-type initial substrate 20 toremove the second thin film layer 120; forming an anti-reflection layer130 on the first surface of the N-type initial substrate 20, and theanti-reflection layer 130 is located on the top surface of the P-typeemitter 10. In some embodiments, the anti-reflection layer 130 may be asingle-layer structure or a multi-layer structure, and the material ofthe anti-reflection layer 130 may be at least one of magnesium fluoride,silicon oxide, aluminum oxide, silicon oxynitride, silicon nitride ortitanium oxide. In some embodiments, the anti-reflection layer 130 maybe formed by a plasma enhanced chemical vapor deposition (PECVD) method.

Referring to FIG. 12 , in some embodiments, the method further includes:forming a first metal electrode 140 being electrically connected to thefirst portion 11 of the P-type emitter 10. The first metal electrode 140is located on the first surface of the N-type initial substrate 20.Since the sheet resistance of the first portion 11 of the P-type emitter10 is low, the first metal electrode 140 is arranged to be electricallyconnected to the first portion 11 of the P-type emitter 10. In this way,the contact resistance between the first metal electrode 140 and thefirst portion 11 of the P-type emitter 10 can be reduced, therebyfacilitating the transport of carriers in the first metal electrode 140penetrating the anti-reflection layer 130. This because the carriers inthe first portion 11 of the P-type emitter 10 and the second portion 12of the P-type emitter 10 will transport to and be collected by the firstmetal electrode 140 in contact with the first portion 11 of the P-typeemitter 10. That is to say, the electrons in the first portion 11 andthe second portion 12 are desired to transport to the first metalelectrode 140 in contact with the first portion 11 of the P-type emitter10. Therefore, the transport of carrier can be greatly improved by theimprovement of the contact resistance between the first metal electrode140 and the first portion 11 of the P-type emitter 10.

In some embodiments, a method for forming the first metal electrode 140includes: printing conductive paste on a top surface of theanti-reflection layer 130 in the preset region, the conductive materialin the conductive paste may be at least one of silver, aluminum, copper,tin, gold, lead or nickel; and sintering the conductive paste, forexample, the sintering may be performed under a peak temperature of 750°C. to 850° C., so as to penetrate the anti-reflection layer 130 to formthe first metal electrode 140.

Referring to FIG. 13 , a tunnel layer 150 and a doped conductive layer160 are formed over a second surface of the N-type substrate 100 in adirection away from the N-type substrate 100.

The tunnel layer 150 is used to realize the interface passivation of thesecond surface of the N-type substrate 100. In some embodiments, thetunnel layer 150 may be formed using a deposition process, such as achemical vapor deposition process. In some other embodiments, the tunnellayer 150 may be formed using an in-situ generation process. As anexample, in some embodiments, the material of the tunnel layer 150 maybe any one of silicon oxide, magnesium fluoride, amorphous silicon,polycrystalline silicon, silicon carbide, silicon nitride, siliconoxynitride, aluminum oxide and titanium oxide.

The doped conductive layer 160 is used to form field passivation. Insome embodiments, the material of the doped conductive layer 160 may bedoped silicon. In some embodiments, the doped conductive layer 160 andthe N-type substrate 100 include doping elements of the sameconductivity type, the doped silicon may include one or more of N-typedoped polysilicon, N-type doped microcrystalline silicon, N-type dopedamorphous silicon and silicon carbide. In some embodiments, the dopedconductive layer 160 may be formed using a deposition process. As anexample, intrinsic polysilicon may be deposited on the surface of thetunnel layer 150 away from the N-type substrate 100 to form apolysilicon layer, and phosphorus ions may be doped in manners of ionimplantation and source diffusion to form an N-type doped polysiliconlayer. The N-type doped polysilicon layer serves as the doped conductivelayer 160.

Referring to FIG. 1 , in some embodiments, the method further includesforming a first passivation layer 170 on a surface of the dopedconductive layer 160 away from the N-type substrate 100. In someembodiments, the material of the first passivation layer 170 may be oneor more of magnesium fluoride, silicon oxide, aluminum oxide, siliconoxynitride, silicon nitride and titanium oxide. In some embodiments, thefirst passivation layer 170 may be a single-layer structure. In someother embodiments, the first passivation layer 170 may be a multi-layerstructure. As an example, in some embodiments, the first passivationlayer 170 may be formed using a PECVD method.

In some embodiments, the method further includes forming a second metalelectrode 180 penetrating the first passivation layer 170 to form anelectrical connection with the doped conductive layer 160. As anexample, the method for forming the second metal electrode 180 may bethe same as the method for forming the first metal electrode 140, andthe material of the first metal electrode 140 may be the same as thematerial of the second metal electrode 180.

In the production method for a solar cell as provided by the aboveembodiments, the at least one edge of each formed first pyramidstructure 1 has irregular deformation, and a spherical or spherical-likesubstructure 14 is formed on each of top surfaces of at least a part ofthe first pyramid structures 1, so that the first pyramid structures 1have micro-defects, and changes in silicon crystals are formed in thefirst portion 11 of the P-type emitter. Furthermore, edges of eachsecond pyramid structure 2 are straight, in other words, there is nodeformation in the edges of each second pyramid structure 2. Due to themicro-defects of the first pyramid structures 1, the sheet resistance ofthe first portion 11 is much less than the sheet resistance of thesecond portion 12, thereby greatly improving ohmic contact of the firstportion 11 of the P-type emitter 10. Meanwhile, the doping concentrationof the first portion 11 of the P-type emitter 10 is kept low, so thatthe generations of recombination centers in the first portion 11 of theP-type emitter 10 can be reduced, the good passivation effect of theP-type emitter 10 can be maintained, and the generations of Augerrecombination can be reduced. In this way, the photoelectric conversionperformance of the solar cell can be improved.

Comparative Example

The comparative example provides a solar cell, including: a substrate;an emitter formed on a first surface of the substrate, the emitterincludes a first portion 11 (refer to FIG. 1 ) and a second portion 12(refer to FIG. 1 ), a top surface of the first portion 11 includes athird pyramid structure whose edges are straight, and a top surface ofthe second portion 12 includes a fourth pyramid structure whose edgesare straight. A doping concentration of the first portion 11 is greaterthan a doping concentration of the second portion 12, and a sheetresistance of the first portion 11 is lower than a sheet resistance ofthe second portion 12.

Compared with the structure of the solar cell according to embodimentsof the present disclosure as shown in FIG. 1 , the difference betweenthe structure of the solar cell according to the comparative example andthat according to the embodiments of the present disclosure lies inthat, in the comparative example, the edges of the third pyramidstructure on the top surface of the first portion are straight. Based oncomparative experiment, the parameters according to the embodiments ofthe present disclosure and those according to the comparative exampleare compared as shown in Table 1:

TABLE 1 Open-circuit Short-circuit Filling Conversion voltage currentdensity factor efficiency Uoc (V) Jsc (mA/cm²) FF (%) Eff (%)Embodiments 0.720 41.81 83.3 25.07 of the present disclosure Comparative0.713 41.62 83.2 24.69 example

It can be seen from Table 1 that, compared with the comparative example,each of the open-circuit voltage, short-circuit current density, fillingfactor and conversion efficiency of the solar cell according toembodiments of the present disclosure is higher, so that the solar cellaccording to embodiments of the present disclosure has a betterconversion performance. It can be seen that, due to the micro-defects ofthe first pyramid structures 1, the sheet resistance of the firstportion 11 (refer to FIG. 1 ) is greatly reduced, thereby greatlyimproving ohmic contact of the first portion 11 of the P-type emitter 10(refer to FIG. 1 ). Meanwhile, the doping concentration of the firstportion 11 of the P-type emitter 10 is relatively low, so that thegenerations of recombination centers in the first portion 11 of theP-type emitter 10 can be reduced, a good passivation effect of theP-type emitter 10 can be maintained, and the generations of Augerrecombination can be reduced. In this way, the photoelectric conversionperformance of the solar cell can be improved.

Although the present disclosure is disclosed above with exemplaryembodiments, they are not used to limit the claims. Any person skilledin the art can make some possible changes and modifications withoutdeparting from the concept of the present disclosure. The scope ofprotection of the present disclosure shall be subject to the scopedefined by the claims.

Those having ordinary skill in the art shall understand that the aboveembodiments are exemplary implementations for realizing the presentdisclosure. In practice, any person skilled in the art to which theembodiments of the present disclosure belong may make any modificationsand changes in forms and details without departing from the scope of thepresent disclosure. Therefore, the patent protection scope of thepresent disclosure shall still be subject to the scope limited by theappended claims.

1. A solar cell, comprising: an N-type substrate; a P-type emitterformed on a first surface of the N-type substrate; and a tunnel layerand a doped conductive layer sequentially formed over a second surfaceof the N-type substrate in a direction away from the N-type substrate;wherein the P-type emitter comprises a first portion and a secondportion, the first portion has first pyramid structures formed on a topsurface of the first portion and the second portion has second pyramidstructures formed on a top surface of the second portion; wherein atransition surface is respectively formed on at least one edge of eachfirst pyramid structure, the at least one edge has irregulardeformation, the transition surface is joined with two adjacent inclinedsurfaces of the each first pyramid structure, and the transition surfaceis concave or convex relative to a center of the each first pyramidstructure; wherein a substructure is formed on each of top surfaces ofat least a part of the first pyramid structures, and a shape of thesubstructure is spherical or spherical-like; wherein edges of eachsecond pyramid structure are straight; and wherein a sheet resistance ofthe first portion ranges from 10 ohm/sq to 500 ohm/sq, a dopingconcentration at the top surface of the first portion ranges from 1E¹⁷atoms/cm³ to 8E¹⁹ atoms/cm³; a sheet resistance of the second portionranges from 100 ohm/sq to 1000 ohm/sq, and a doping concentration at thetop surface of the second portion ranges from 1E¹⁶ atoms/cm³ to 5E¹⁹atoms/cm³.
 2. The solar cell according to claim 1, wherein heights ofthe first pyramid structures range from 0.1 μm to 5 μm, and sizes ofbottoms of the first pyramid structures range from 0.5 μm to 5 μm in anyone dimension.
 3. The solar cell according to claim 1, wherein a dopingelement in the first portion of the P-type emitter is of a sameconductivity type as a doping element in the second portion of theP-type emitter, and the doping element in the first portion and thedoping element in the second portion are each a trivalent element, andwherein the doping element in the first portion and the doping elementin the second portion each comprise boron or gallium.
 4. The solar cellaccording to claim 1, wherein the sheet resistance of the first portionis lower than the sheet resistance of the second portion.
 5. The solarcell according to claim 1, wherein the doping concentration at the topsurface of the first portion is not less than the doping concentrationat the top surface of the second portion.
 6. The solar cell according toclaim 1, wherein a junction depth of the first portion is not less thana junction depth of the second portion.
 7. The solar cell according toclaim 6, wherein a ratio of the junction depth of the first portion tothe junction depth of the second portion is not less than 2, and whereinthe junction depth of the first portion ranges from 0.2 μm to 10 μm, andthe junction depth of the second portion ranges from 0.05 μm to 5 μm. 8.The solar cell according to claim 1, wherein a difference between thedoping concentration at the top surface of the first portion and adoping concentration at a bottom surface of the first portion rangesfrom 8E¹⁹ atoms/cm³ to 1E¹⁷ atoms/cm³, and wherein a difference betweenthe doping concentration at the top surface of the second portion and adoping concentration at a bottom surface of the second portion rangesfrom 5E¹⁹ atoms/cm³ to 1E¹⁶ atoms/cm³.
 9. The solar cell according toclaim 1, wherein at least a part of at least one inclined surface of theeach first pyramid structure is concave or convex relative to a centerof the each first pyramid structure.
 10. The solar cell according toclaim 1, further comprising a first metal electrode, wherein the firstmetal electrode is formed on the first surface of the N-type substrate,and is electrically connected to the first portion of the P-typeemitter, and wherein a width of the first metal electrode is less thanor equal to a width of the first portion of the P-type emitter.
 11. Aphotovoltaic module, comprising: a cell string including a plurality ofsolar cells, wherein the plurality of solar cells are electricallyconnected in sequence; an encapsulation layer configured to cover asurface of the cell string; and a cover plate configured to cover asurface of the encapsulation layer facing away from the cell string;wherein each of the plurality of solar cells comprise: an N-typesubstrate; a P-type emitter formed on a first surface of the N-typesubstrate; and a tunnel layer and a doped conductive layer sequentiallyformed over a second surface of the N-type substrate in a direction awayfrom the N-type substrate; wherein the P-type emitter comprises a firstportion and a second portion, the first portion has first pyramidstructures formed on a top surface of the first portion and the secondportion has second pyramid structures formed on a top surface of thesecond portion; wherein a transition surface is respectively formed onat least one edge of each first pyramid structure, the at least one edgehas irregular deformation, the transition surface is joined with twoadjacent inclined surfaces of the each first pyramid structure, and thetransition surface is concave or convex relative to a center of the eachfirst pyramid structure; wherein a substructure is formed on each of topsurfaces of at least a part of the first pyramid structures, and a shapeof the substructure is spherical or spherical-like; wherein edges ofeach second pyramid structure are straight; and wherein a sheetresistance of the first portion ranges from 10 ohm/sq to 500 ohm/sq, adoping concentration at the top surface of the first portion ranges from1E¹⁷ atoms/cm³ to 8E¹⁹ atoms/cm³; a sheet resistance of the secondportion ranges from 100 ohm/sq to 1000 ohm/sq, and a dopingconcentration at the top surface of the second portion ranges from 1E¹⁶atoms/cm³ to 5E¹⁹ atoms/cm³.
 12. The photovoltaic module according toclaim 11, wherein heights of the first pyramid structures range from 0.1μm to 5 μm, and sizes of bottoms of the first pyramid structures rangefrom 0.5 μm to 5 μm in any one dimension.
 13. The photovoltaic moduleaccording to claim 11, wherein a doping element in the first portion ofthe P-type emitter is of a same conductivity type as a doping element inthe second portion of the P-type emitter, and the doping element in thefirst portion and the doping element in the second portion are each atrivalent element, and wherein the doping element in the first portionand the doping element in the second portion each comprise boron orgallium.
 14. The photovoltaic module according to claim 11, wherein thesheet resistance of the first portion is lower than the sheet resistanceof the second portion.
 15. The photovoltaic module according to claim11, wherein the doping concentration at the top surface of the firstportion is not less than the doping concentration at the top surface ofthe second portion.
 16. The photovoltaic module according to claim 11,wherein a junction depth of the first portion is not less than ajunction depth of the second portion.
 17. The photovoltaic moduleaccording to claim 16, wherein a ratio of the junction depth of thefirst portion to the junction depth of the second portion is not lessthan 2, and wherein the junction depth of the first portion ranges from0.2 μm to 10 μm, and the junction depth of the second portion rangesfrom 0.05 μm to 5 μm.
 18. The photovoltaic module according to claim 11,wherein a difference between the doping concentration at the top surfaceof the first portion and a doping concentration at a bottom surface ofthe first portion ranges from 8E¹⁹ atoms/cm³ to 1E¹⁷ atoms/cm³, andwherein a difference between the doping concentration at the top surfaceof the second portion and a doping concentration at a bottom surface ofthe second portion ranges from 5E¹⁹ atoms/cm³ to 1E¹⁶ atoms/cm³.
 19. Thephotovoltaic module according to claim 11, wherein at least a part of atleast one inclined surface of the each first pyramid structure isconcave or convex relative to a center of the each first pyramidstructure.
 20. The photovoltaic module according to claim 11, whereineach of the plurality of solar cells further comprise a first metalelectrode, wherein the first metal electrode is formed on the firstsurface of the N-type substrate, and is electrically connected to thefirst portion of the P-type emitter, and wherein a width of the firstmetal electrode is less than or equal to a width of the first portion ofthe P-type emitter.